Process of producing pulp high in resistant crllulose



Oct. 12 1926.

G; A. RICHTERl PROCESS OF PRODUCING PULVP HIGH IN RESISTANT CEIJLULOSE Filed Nov. 1l, 1924 @S www Q@ Patented ou. 12, 1926.

UNITED STATES PATENT OFFICE GEORGE A. RICHTER, I' BERLIN, NEW HAHPSHIBE, ABSIGNOR TO BROWN COMPANY, 0l' BERLIN, NEW 'HAHPSHIBE A CORPORATION 0l' MAINE.

IPEOQESB 0l' PBODUCING PULP HIGHV IN RESISTANT CELLULOSE.

appnoguan ma November 11, 11m. ,serial no. 749,215.

. This invention has relation to the production of cellulose pul from wood, and has particularly for its o ject the production of wood pulp, having a high alpha cellulose content. The invention has further for its object to provide a process which is economical and 1n. which certain other advantages are attained as will be subsequently explained in detail.` The process which I shall herein describe is practiced in those plants where both sulphite and soda or sulphate pulps are produced.

In accordance with the present invention, the p which is produced by the acid sulul 15 hite digestion, is 'treated with the black iquor resultin from the alkaline digestion, as a result o which results are achieved `which have not heretofore been possible.

On the accompanyin drawing, I have il- 20 lustrated conventional y apparatus which ly an acid sul hite digester in which spruce c or other suita le wood chips are cooked in an acid sulphite` solution' of" sullicient strength, under conditions of temperature and pressure, until the cellulose liber is freed 40' from the encrusting or eementitious part of the wood. The strength of the acid solution@ will depend uponv circumstances, .but ordinarily I refer a solution containing, say, 5% free S 2 and 1%'combined SO2. After the cooking operationis completed,the pulp and the waste liquor are blown into a blowV pit indicated at 2, this being the normal operation followed in the'I acid digestion of wood. InA the blew pit the waste acid Vliquor and the pulp are separated, the wasteliquor bein fconducted from the 'blow' pit.

b a conduit indicated conventionally at 3.

rom the blow pit the cellulose pulp is de-f' livered to a treating tank indicated at 4, -Wherein it is subjected to reaction with an alkaline liquor derived from the alkaline digestion of wood pulp. This alkaline'digestlon 1s carried on in a digester indicated at 5 wherein the wood chips are subjected tothe action of an alkaline cooking liquor' such as caustic soda or a solution containing caustic soda and sodium sulphide. When the caustic soda alone is employed as the cooking agent, the resulting cellulose product 1s commonly termed the soda pulp; but, when the alkaline cooking includes in addition to caustic soda a certain proportion of sodium sulphide, the cellulosic product resultmg therefrom is commonly termed sulphate pulp or kraft pulp. After the ulp 1n digcster 5 has been subjected to a cooliing operation under hightemperature and prese.

sure for a suilicient length of time, the contents'of the digester are delivered toa'blow pit indicated at 6, from which both thelpulp andthe black liquor are delivered to a washv er 7 in which the pulp is separated from the black liquor and 1s washed by the countercurrent system. I preferably employl a washer of the t pe shown in Letters Patent No. 1,421,664, ated July 4, 1922,- in which a small amount of water kis delivered to the washer by a pipe 8 at the same end of the washer from w ich the washed pulp is delivered. The black liquor is delivered'from the washer throu h a conduit 9, and, as it is but slightly dgiluted by incoming wash water throughconduit 8 and is at a high temperature, a portion thereof may be used in' carrying on the digestion of the next batch of wood chips in digester 5. Consequently I have shown leading from the conduit 9 a conduit 10 by which a part of the black liquor is delivered to the upper end of digester 5. to be commingled withl the fresh alkaline cooking liquor which is fed into the digester 5 after the chips have been placed therein. The black liquor emerging from the washer -7 is of a temperature of. approximate? from kto 190 F., and may have a ree alkaline content of as high as 1%. I employ this black' liquor, previous to the recovery of the soda-content therefrom, in treating thepulp produced by the `acid digestion and whlch as previously stated is collected in tank 4. Cons' ue1...y the conduit 9 is connected with the tank 4' so as to deliver-thereto the measured necessary volume to furnish the alkali necessary forthe treatmenteof the pulp contained in said tank. The purpose of treating the sulphite pulp contained in tank 4 is the removal of the greater portion of the less resistant cellulose,-the.beta and gamma cellulose,--as well as the removal of lignin, resin and pentosan contained in the pulp. These materials are dissolved in the alkaline solution together with the greater portion of the less resistant cellulose. The presence in the waste liquor of the organic constituents resulting from the previous alkaline digestion of the pulp in digester 5 does not interfere in any way with the dissolving and removal. of the less resistant cellulose, the lignin, the resin and the pentosan. The temperature of the waste alkaline blalck liquor is suicient to cause the dissolving of the substances which I have mentioned, but, if desired, to speed the reaction, the tank 4 may be heated to a'liigher temperature by any suitable means. In' some cases, it may be desirable to maintain the temperature of' the alkaline solution at its boiling point. The tank 4 is also preferably provided with agitating mechanism to ensure the thorough commingling of the hot blackliquor with the -pulp which is therein contained, and I have lshown conventionally the tank as being provided with an agitator' indicated at 25 for this purpose. After the pulp, in the' tank 4 has been subjected vto hot alkaline treatment, it is now ready to be washed and recovered, but at the same time I desire also to recover the black liquor in order that its-valuable sodiumcompounds may be recovered for reuse in the production of an a1- kaline cookin liquor. For this purpose the pulp and alka ine liquor-are drawn from the tank 4 and delivered to a washer 11 of the counter-current type. This washer is of the same class as that indicated at 7 4in which the pulp is delivered at one end of the. in-

strumentality and the wash water at the other, and the two caused to pass in countercurrent flow. A small amount of warm water is fed tothe washer through a pipe 12 and the content/s .of tank 4 are delivered to the other end of the washer by -a conduit 13; 'The washed pulp, which is now characterized by a high alp a cellulose content and a minimum proportion of beta and gamma cellulose, lignin, resin and pentosan, and

-which is also freed from the organic content of the black liquor bythe washing operation, is delivered from the washer to tank 14. To this pulp may now be added suiicient bisulphite antichlor. to neutralize any residual 'traces of alkali that may re main in the pulp. The pulp, if desired, may

now be passed from the tank`14 through a conduit 15 to any suitable bleaching apparatus indicated conventionally at 16 for further bleaching and whitening of the pulp. The black liquor, together withthe small amount of wash water which is added to the washer l1, is withdrawn from the washer through conduit 17 and is subjected to concentration and evaporation until it is of about the .consistency of treacle. Inasmuch as there may be delivered from the alkaline digestea quantity of black liquor in excess of that needed for the alkaline treatment of the sulphite pulp, a portion of the black liquor ,from the washer 7 may be diverted from the conduit 9 and delivered to the evaporator or concentrator. together with the spent liquor from the washer 11. At 18 I have indicated conventionally a concentrating and evaporat'ing apparatus which may be of the multiple-effect type. The concentrated alkaline liquor, containing such organic compounds as were derived from the sulphite pulp, is now fed to a retort or furnace, and the soda content of the liquor is recovered therefrom in molten condition. In the event that the alkaline liquor employed in the alkaline digestion is one comprising sodium sulphide, a reduc'n dium sulphide; but, if the alkaline cooking liquor consists only of caustic soda, an oxidizing atmosphere may be maintained in the furnace so that the soda is recovered in the form of sodium carbonate. Any additional make-up materials which may be needed, such as sodium sulphate. or sodium carbonate, may be added to the evaporated liquor before it is subjected to the smelting operation.

vAt 19 I have indicated conventionally a furnace or retort and at 20 a dissolving tank into which the smelted sodium compounds are delivered from the furnace 1 9. This tank contains an alkaline liquor 1n which the sodium compounds are dissolved. At 21 .I have indicated the usual causticizing tank into which the solution from the dissolving tank is delivered, in which the liquor is caustici'zed by the addition of a Suf- 'icent quantity of lime to react with the 'l filtrate beingv conducted by a conduit 23 to a storage tank 24 from which it is drawn 4as needed for cooking wood chips in the alkaline digester 5. i

Whereas I have shown only a single alkaline digester and a single sulphite digester, it will be ofcourse understood that-I ma have any number of such digesters whic will be blown in succession, so that the process whichI have herein .described is carried Aon continuously instead of intermittently.

That is to say, the supply of. pulp from the which itself is highly desirable,-the process which VI have hereindescribed is .highly advantageous in certain other respects,v

several of which ma be mentioned. By

utilizing a portion o the blackliquonderived from the alkaline digestion in supplying the alkali necessary for treating the sulphite pulp, there is a marked conservation' of heat inasmuch as the black liquor delivered4 from the blow pit and the Washer 7 -is at a high temperature, so that but little heat is, needed to maintain this or an even higher temperature in the digestion tank 4. Furthermore the alkali required in the digestion of sulphite pulp does not represent a loss of chemical constituents inasmuch as this alkali is. subse uently recovered. Moreover the liquor Whidii is returned from the Washer 11 has been enriched in organic constituents which are combustible and which therefore increase the combustible characteristic of the original black liquor. Consequently, inasmuch as theblack liquor which is 110W fed to the combustion retort has an increased.

1,092, ses

quantity-of combustible matter, it allows a more vcomplete reduction of sodium sulphate in the event that it is .desired to produce sulphate or kraft pulp. Z

What I claim is: 1. A process -such as herein described.

which comprises treating sulphite puli'rwith alkaline black liquor resulting from the alkaline digestion of wood.

2. A process such as. herein described, which comprisesv treating sulphite pulp with alkaline black liquor resulting from the alkaline digestion of Wood, separa-ting such pulp .from the alkaline liquor, and recoveringthe sodium components of said liquor.

3. A process such as herein described,

which comprises digesting/Wood withA an alkaline cooking liquor, separating the hot Waste liquor from'the pulp, and treating sulphite'pulpy with such hot Waste liquor.

4.-. A process such as herein described, which comprises digesting wood with an alkaline cooking liquor, Washing such pulp and separating the -hot black liquor therefrom, treating sulphite pulp with said recovered hot alkaline black liquor, separating the-alkaline black liquor from s uch pulp,

and concentrating and burning the combusv v til-le content of such black liquor and recovering the sodium components thereof.`

In testimony whereof I have aiiixed my signature.

GEORGE A. RICHTER. 

